Making rimmed steel



Patented Dec. 14, 1937 I UNITEDISITATIES PATENT ()FFICE MAKING RIMIWED STEEL Rufus E. Zimmerman, Short Hills, N. .l., and Clarence D. King, Brooklyn, N. T

No Drawing. Application January 8, 1937, Serial No. 119,630

3 Claims. (01. 7553) Rimmed or efiervescingsteel is particularly and that such agents are particularly effective valuable in steel products requiring ductility and in the more diiiicult steels referred to above conthe ingots of such steel are characterized chiefly taining .20 per cent or more carbon and having by a skin which for a considerable depth, one an unusually low iron oxide content. Commerto two inches, is uniform and dense and excepcial borax may be used having the formula tionally clean or freefrom blow holes so that it Na2B4O1JOHzO. It should be dehydrated to rerolls well. move all or most of the 10% molecules of water The process of rimming is characterized by a of crystallization by heating to 500 degrees C. or boiling or an escape of gases during the solidifihigher, as by roasting, fusing or sintering or the cation of the ingot in the mold, as distinguished like. Or borax glass may be used, or a mixture from killed or partly killed steel which is quiesof ordinary glass, comprising sodium and calcium cent in the mold. silicates, with boric acid or borax, may be used. For the best results the rimming or ebullition The quantity used may be varied from one ounce should be regular and fairly long continued, as to one pound of borax per ton of steel. It may distinguished from spasmodic escape of large be added, wholly or in part, in the ladle but is bubbles of gas. preferably introduced into the ingot mold while Rimming steels generally have been of low carpouring, shortly after beginning the teeming opbon content, below about .20 carbon (and in eration., larger part below .10 carbon) and containing in For example, we have found that the add tion the molten condition when tapped from the furof dehydrated commercial borax to the extent nace a fairly high percentage of iron oxide of two or three ounces per ton of ingot results (FeO); the evolution of the escaping gases be: in good rimming action in steels which inhering apparently caused by the generation of carently lack this characteristic, such as steels conbon monoxide in the molten metal. taining .20 carbon and higher, with a decided In the very low carbon steels (.05 carbon and improvement in the rolling characteristics of the under) there normally exists sufiicient iron oxide product, better surface, less rejections of mateto assure maximum reaction with carbon when rial and less chipping or reconditioning of the pouring the heat, and maximum rimming action, partially rolled steel, and less scrap. permitting the gases in the steel to escape freely In the rimming operation there is normally a and assuring proper thickness of good skin and drop in the top level of the ingot during the early location Of w e It s more diflicult to prostages of solidification. There is generally a rise duce constantly a properly rimmed ingot, that of the top level as the steel freezes; the better is, one with desired skin thickness and location the rimming action, the smaller the rise. of blow holes, with comparatively high carbon Taking steels which are generally recognized steels, say from .20 to .35 percent carbon. as most diflicult to rim, running from .23 to .30 Steels with comparatively low iron oxide concarbon and adding borax from about one and tent are also more difficult to rim properly, as one-quarter ounces to three ounces per ton of are those of high manganese content and those ingot, we have secured a good rimming action tapped at high temperatures; and comparatively with a growth of the ingot at the end of less large ingots present a special difliculty because than three inches and in nearly all cases less the rimming action is not as pronounced as in than two inches, which is good rimming practhe casting of small ingots. With these ccmpotice. Photomicrographs of sections of the blooms, sitions and these conditions thin skinned inbillets and bars rolled from these ingots showed gots often result with blow holes close to the surthat the blow holes had been favorably seated,

, 'face. Frequently such blow holes are exposed that is, in the middle portion of the rolled prodon heating in soaking pits prior to rolling, renets, with the desired pattern of the skin or case sulting in defects in the steel when rolled. They and the core such as are found in good rimmed are also objectionable in the finished product steel.

because of their close proximity to the surfaces The quantity of the boric-acid-containing or of the steel. borax-containing agent may be varied and can We have discovered that the rimming operabe readily adjusted to the most economical point tion can be improved and the quality of the to produce the best rimming ingot in accordance rimmed steel bettered by the addition of a borate with the conditions referred to above. In addsuch as borax or borlc-acid or a borax glass or ing the agent to the molds the commonly preother boron-oxygen compounds after tapping ferred practice is to introduce it near the botamazes metal to the molten steel while pouring the ingot.

2. The method of rimming steel containing carbon over .20 per cent which comprises the addition to the molten steel after tapping of a small percentage (of the order of a few ounces per ton of steel) of a member of the group consisting of boric-acid and the borates.

3. The method of rimming steel containing carbon over .20 per cent which comprises the addition to the molten steel while pouring the 1 ingot of about 2 or 3 ounces of dehydrated borax per ton of steel.

, RUFUS E. ZIMMERMAN.

CLARENCE D. ENG, 

